/*
 * Copyright (c) 1991, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *  @(#)queue.h 8.5 (Berkeley) 8/20/94
 */

#ifndef _SYS_QUEUE_H_
#define _SYS_QUEUE_H_

/*
 * This file defines five types of data structures: singly-linked lists,
 * lists, simple queues, tail queues, and circular queues.
 *
 * A singly-linked list is headed by a single forward pointer. The
 * elements are singly linked for minimum space and pointer manipulation
 * overhead at the expense of O(n) removal for arbitrary elements. New
 * elements can be added to the list after an existing element or at the
 * head of the list.  Elements being removed from the head of the list
 * should use the explicit macro for this purpose for optimum
 * efficiency. A singly-linked list may only be traversed in the forward
 * direction.  Singly-linked lists are ideal for applications with large
 * datasets and few or no removals or for implementing a LIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may only be traversed in the forward direction.
 *
 * A simple queue is headed by a pair of pointers, one the head of the
 * list and the other to the tail of the list. The elements are singly
 * linked to save space, so elements can only be removed from the
 * head of the list. New elements can be added to the list after
 * an existing element, at the head of the list, or at the end of the
 * list. A simple queue may only be traversed in the forward direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * A circle queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or after
 * an existing element, at the head of the list, or at the end of the list.
 * A circle queue may be traversed in either direction, but has a more
 * complex end of list detection.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
 * _HEAD                +       +       +       +       +
 * _HEAD_INITIALIZER    +       +       +       +       +
 * _ENTRY               +       +       +       +       +
 * _INIT                +       +       +       +       +
 * _EMPTY               +       +       +       +       +
 * _FIRST               +       +       +       +       +
 * _NEXT                +       +       +       +       +
 * _PREV                -       -       -       +       +
 * _LAST                -       -       +       +       +
 * _FOREACH             +       +       +       +       +
 * _FOREACH_REVERSE     -       -       -       +       +
 * _INSERT_HEAD         +       +       +       +       +
 * _INSERT_BEFORE       -       +       -       +       +
 * _INSERT_AFTER        +       +       +       +       +
 * _INSERT_TAIL         -       -       +       +       +
 * _REMOVE_HEAD         +       -       +       -       -
 * _REMOVE              +       +       +       +       +
 */

/*
 * List definitions.
 */
#define LIST_HEAD(name, type)                                                  \
  struct name {                                                                \
    struct type* lh_first; /* first element */                                 \
  }

#define LIST_HEAD_INITIALIZER(head)                                            \
  { NULL }

#define LIST_ENTRY(type)                                                       \
  struct {                                                                     \
    struct type* le_next;  /* next element */                                  \
    struct type** le_prev; /* address of previous next element */              \
  }

/*
 * List functions.
 */
#define LIST_INIT(head)                                                        \
  do {                                                                         \
    (head)->lh_first = NULL;                                                   \
  } while (/*CONSTCOND*/ 0)

#define LIST_INSERT_AFTER(listelm, elm, field)                                 \
  do {                                                                         \
    if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)             \
      (listelm)->field.le_next->field.le_prev = &(elm)->field.le_next;         \
    (listelm)->field.le_next = (elm);                                          \
    (elm)->field.le_prev     = &(listelm)->field.le_next;                      \
  } while (/*CONSTCOND*/ 0)

#define LIST_INSERT_BEFORE(listelm, elm, field)                                \
  do {                                                                         \
    (elm)->field.le_prev      = (listelm)->field.le_prev;                      \
    (elm)->field.le_next      = (listelm);                                     \
    *(listelm)->field.le_prev = (elm);                                         \
    (listelm)->field.le_prev  = &(elm)->field.le_next;                         \
  } while (/*CONSTCOND*/ 0)

#define LIST_INSERT_HEAD(head, elm, field)                                     \
  do {                                                                         \
    if (((elm)->field.le_next = (head)->lh_first) != NULL)                     \
      (head)->lh_first->field.le_prev = &(elm)->field.le_next;                 \
    (head)->lh_first     = (elm);                                              \
    (elm)->field.le_prev = &(head)->lh_first;                                  \
  } while (/*CONSTCOND*/ 0)

#define LIST_REMOVE(elm, field)                                                \
  do {                                                                         \
    if ((elm)->field.le_next != NULL)                                          \
      (elm)->field.le_next->field.le_prev = (elm)->field.le_prev;              \
    *(elm)->field.le_prev = (elm)->field.le_next;                              \
  } while (/*CONSTCOND*/ 0)

#define LIST_FOREACH(var, head, field)                                         \
  for ((var) = ((head)->lh_first); (var); (var) = ((var)->field.le_next))

/*
 * List access methods.
 */
#define LIST_EMPTY(head) ((head)->lh_first == NULL)
#define LIST_FIRST(head) ((head)->lh_first)
#define LIST_NEXT(elm, field) ((elm)->field.le_next)

/*
 * Singly-linked List definitions.
 */
#define SLIST_HEAD(name, type)                                                 \
  struct name {                                                                \
    struct type* slh_first; /* first element */                                \
  }

#define SLIST_HEAD_INITIALIZER(head)                                           \
  { NULL }

#define SLIST_ENTRY(type)                                                      \
  struct {                                                                     \
    struct type* sle_next; /* next element */                                  \
  }

/*
 * Singly-linked List functions.
 */
#define SLIST_INIT(head)                                                       \
  do {                                                                         \
    (head)->slh_first = NULL;                                                  \
  } while (/*CONSTCOND*/ 0)

#define SLIST_INSERT_AFTER(slistelm, elm, field)                               \
  do {                                                                         \
    (elm)->field.sle_next      = (slistelm)->field.sle_next;                   \
    (slistelm)->field.sle_next = (elm);                                        \
  } while (/*CONSTCOND*/ 0)

#define SLIST_INSERT_HEAD(head, elm, field)                                    \
  do {                                                                         \
    (elm)->field.sle_next = (head)->slh_first;                                 \
    (head)->slh_first     = (elm);                                             \
  } while (/*CONSTCOND*/ 0)

#define SLIST_REMOVE_HEAD(head, field)                                         \
  do {                                                                         \
    (head)->slh_first = (head)->slh_first->field.sle_next;                     \
  } while (/*CONSTCOND*/ 0)

#define SLIST_REMOVE(head, elm, type, field)                                   \
  do {                                                                         \
    if ((head)->slh_first == (elm)) {                                          \
      SLIST_REMOVE_HEAD((head), field);                                        \
    } else {                                                                   \
      struct type* curelm = (head)->slh_first;                                 \
      while (curelm->field.sle_next != (elm)) curelm = curelm->field.sle_next; \
      curelm->field.sle_next = curelm->field.sle_next->field.sle_next;         \
    }                                                                          \
  } while (/*CONSTCOND*/ 0)

#define SLIST_FOREACH(var, head, field)                                        \
  for ((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)

/*
 * Singly-linked List access methods.
 */
#define SLIST_EMPTY(head) ((head)->slh_first == NULL)
#define SLIST_FIRST(head) ((head)->slh_first)
#define SLIST_NEXT(elm, field) ((elm)->field.sle_next)

/*
 * Singly-linked Tail queue declarations.
 */
#define STAILQ_HEAD(name, type)                                                \
  struct name {                                                                \
    struct type* stqh_first; /* first element */                               \
    struct type** stqh_last; /* addr of last next element */                   \
  }

#define STAILQ_HEAD_INITIALIZER(head)                                          \
  { NULL, &(head).stqh_first }

#define STAILQ_ENTRY(type)                                                     \
  struct {                                                                     \
    struct type* stqe_next; /* next element */                                 \
  }

/*
 * Singly-linked Tail queue functions.
 */
#define STAILQ_INIT(head)                                                      \
  do {                                                                         \
    (head)->stqh_first = NULL;                                                 \
    (head)->stqh_last  = &(head)->stqh_first;                                  \
  } while (/*CONSTCOND*/ 0)

#define STAILQ_INSERT_HEAD(head, elm, field)                                   \
  do {                                                                         \
    if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)                 \
      (head)->stqh_last = &(elm)->field.stqe_next;                             \
    (head)->stqh_first = (elm);                                                \
  } while (/*CONSTCOND*/ 0)

#define STAILQ_INSERT_TAIL(head, elm, field)                                   \
  do {                                                                         \
    (elm)->field.stqe_next = NULL;                                             \
    *(head)->stqh_last     = (elm);                                            \
    (head)->stqh_last      = &(elm)->field.stqe_next;                          \
  } while (/*CONSTCOND*/ 0)

#define STAILQ_INSERT_AFTER(head, listelm, elm, field)                         \
  do {                                                                         \
    if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)         \
      (head)->stqh_last = &(elm)->field.stqe_next;                             \
    (listelm)->field.stqe_next = (elm);                                        \
  } while (/*CONSTCOND*/ 0)

#define STAILQ_REMOVE_HEAD(head, field)                                        \
  do {                                                                         \
    if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL)    \
      (head)->stqh_last = &(head)->stqh_first;                                 \
  } while (/*CONSTCOND*/ 0)

#define STAILQ_REMOVE(head, elm, type, field)                                  \
  do {                                                                         \
    if ((head)->stqh_first == (elm)) {                                         \
      STAILQ_REMOVE_HEAD((head), field);                                       \
    } else {                                                                   \
      struct type* curelm = (head)->stqh_first;                                \
      while (curelm->field.stqe_next != (elm))                                 \
        curelm = curelm->field.stqe_next;                                      \
      if ((curelm->field.stqe_next =                                           \
               curelm->field.stqe_next->field.stqe_next) == NULL)              \
        (head)->stqh_last = &(curelm)->field.stqe_next;                        \
    }                                                                          \
  } while (/*CONSTCOND*/ 0)

#define STAILQ_FOREACH(var, head, field)                                       \
  for ((var) = ((head)->stqh_first); (var); (var) = ((var)->field.stqe_next))

#define STAILQ_CONCAT(head1, head2)                                            \
  do {                                                                         \
    if (!STAILQ_EMPTY((head2))) {                                              \
      *(head1)->stqh_last = (head2)->stqh_first;                               \
      (head1)->stqh_last  = (head2)->stqh_last;                                \
      STAILQ_INIT((head2));                                                    \
    }                                                                          \
  } while (/*CONSTCOND*/ 0)

/*
 * Singly-linked Tail queue access methods.
 */
#define STAILQ_EMPTY(head) ((head)->stqh_first == NULL)
#define STAILQ_FIRST(head) ((head)->stqh_first)
#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)

/*
 * Simple queue definitions.
 */
#define SIMPLEQ_HEAD(name, type)                                               \
  struct name {                                                                \
    struct type* sqh_first; /* first element */                                \
    struct type** sqh_last; /* addr of last next element */                    \
  }

#define SIMPLEQ_HEAD_INITIALIZER(head)                                         \
  { NULL, &(head).sqh_first }

#define SIMPLEQ_ENTRY(type)                                                    \
  struct {                                                                     \
    struct type* sqe_next; /* next element */                                  \
  }

/*
 * Simple queue functions.
 */
#define SIMPLEQ_INIT(head)                                                     \
  do {                                                                         \
    (head)->sqh_first = NULL;                                                  \
    (head)->sqh_last  = &(head)->sqh_first;                                    \
  } while (/*CONSTCOND*/ 0)

#define SIMPLEQ_INSERT_HEAD(head, elm, field)                                  \
  do {                                                                         \
    if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)                   \
      (head)->sqh_last = &(elm)->field.sqe_next;                               \
    (head)->sqh_first = (elm);                                                 \
  } while (/*CONSTCOND*/ 0)

#define SIMPLEQ_INSERT_TAIL(head, elm, field)                                  \
  do {                                                                         \
    (elm)->field.sqe_next = NULL;                                              \
    *(head)->sqh_last     = (elm);                                             \
    (head)->sqh_last      = &(elm)->field.sqe_next;                            \
  } while (/*CONSTCOND*/ 0)

#define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field)                        \
  do {                                                                         \
    if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)           \
      (head)->sqh_last = &(elm)->field.sqe_next;                               \
    (listelm)->field.sqe_next = (elm);                                         \
  } while (/*CONSTCOND*/ 0)

#define SIMPLEQ_REMOVE_HEAD(head, field)                                       \
  do {                                                                         \
    if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL)       \
      (head)->sqh_last = &(head)->sqh_first;                                   \
  } while (/*CONSTCOND*/ 0)

#define SIMPLEQ_REMOVE(head, elm, type, field)                                 \
  do {                                                                         \
    if ((head)->sqh_first == (elm)) {                                          \
      SIMPLEQ_REMOVE_HEAD((head), field);                                      \
    } else {                                                                   \
      struct type* curelm = (head)->sqh_first;                                 \
      while (curelm->field.sqe_next != (elm)) curelm = curelm->field.sqe_next; \
      if ((curelm->field.sqe_next = curelm->field.sqe_next->field.sqe_next) == \
          NULL)                                                                \
        (head)->sqh_last = &(curelm)->field.sqe_next;                          \
    }                                                                          \
  } while (/*CONSTCOND*/ 0)

#define SIMPLEQ_FOREACH(var, head, field)                                      \
  for ((var) = ((head)->sqh_first); (var); (var) = ((var)->field.sqe_next))

/*
 * Simple queue access methods.
 */
#define SIMPLEQ_EMPTY(head) ((head)->sqh_first == NULL)
#define SIMPLEQ_FIRST(head) ((head)->sqh_first)
#define SIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)

/*
 * Tail queue definitions.
 */
#define _TAILQ_HEAD(name, type, qual)                                          \
  struct name {                                                                \
    qual type* tqh_first;      /* first element */                             \
    qual type* qual* tqh_last; /* addr of last next element */                 \
  }
#define TAILQ_HEAD(name, type) _TAILQ_HEAD(name, struct type, )

#define TAILQ_HEAD_INITIALIZER(head)                                           \
  { NULL, &(head).tqh_first }

#define _TAILQ_ENTRY(type, qual)                                               \
  struct {                                                                     \
    qual type* tqe_next;       /* next element */                              \
    qual type* qual* tqe_prev; /* address of previous next element */          \
  }
#define TAILQ_ENTRY(type) _TAILQ_ENTRY(struct type, )

/*
 * Tail queue functions.
 */
#define TAILQ_INIT(head)                                                       \
  do {                                                                         \
    (head)->tqh_first = NULL;                                                  \
    (head)->tqh_last  = &(head)->tqh_first;                                    \
  } while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_HEAD(head, elm, field)                                    \
  do {                                                                         \
    if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)                   \
      (head)->tqh_first->field.tqe_prev = &(elm)->field.tqe_next;              \
    else                                                                       \
      (head)->tqh_last = &(elm)->field.tqe_next;                               \
    (head)->tqh_first     = (elm);                                             \
    (elm)->field.tqe_prev = &(head)->tqh_first;                                \
  } while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_TAIL(head, elm, field)                                    \
  do {                                                                         \
    (elm)->field.tqe_next = NULL;                                              \
    (elm)->field.tqe_prev = (head)->tqh_last;                                  \
    *(head)->tqh_last     = (elm);                                             \
    (head)->tqh_last      = &(elm)->field.tqe_next;                            \
  } while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field)                          \
  do {                                                                         \
    if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)           \
      (elm)->field.tqe_next->field.tqe_prev = &(elm)->field.tqe_next;          \
    else                                                                       \
      (head)->tqh_last = &(elm)->field.tqe_next;                               \
    (listelm)->field.tqe_next = (elm);                                         \
    (elm)->field.tqe_prev     = &(listelm)->field.tqe_next;                    \
  } while (/*CONSTCOND*/ 0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field)                               \
  do {                                                                         \
    (elm)->field.tqe_prev      = (listelm)->field.tqe_prev;                    \
    (elm)->field.tqe_next      = (listelm);                                    \
    *(listelm)->field.tqe_prev = (elm);                                        \
    (listelm)->field.tqe_prev  = &(elm)->field.tqe_next;                       \
  } while (/*CONSTCOND*/ 0)

#define TAILQ_REMOVE(head, elm, field)                                         \
  do {                                                                         \
    if (((elm)->field.tqe_next) != NULL)                                       \
      (elm)->field.tqe_next->field.tqe_prev = (elm)->field.tqe_prev;           \
    else                                                                       \
      (head)->tqh_last = (elm)->field.tqe_prev;                                \
    *(elm)->field.tqe_prev = (elm)->field.tqe_next;                            \
  } while (/*CONSTCOND*/ 0)

#define TAILQ_FOREACH(var, head, field)                                        \
  for ((var) = ((head)->tqh_first); (var); (var) = ((var)->field.tqe_next))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)                      \
  for ((var) = (*(((struct headname*) ((head)->tqh_last))->tqh_last)); (var);  \
       (var) = (*(((struct headname*) ((var)->field.tqe_prev))->tqh_last)))

#define TAILQ_CONCAT(head1, head2, field)                                      \
  do {                                                                         \
    if (!TAILQ_EMPTY(head2)) {                                                 \
      *(head1)->tqh_last                 = (head2)->tqh_first;                 \
      (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last;                  \
      (head1)->tqh_last                  = (head2)->tqh_last;                  \
      TAILQ_INIT((head2));                                                     \
    }                                                                          \
  } while (/*CONSTCOND*/ 0)

/*
 * Tail queue access methods.
 */
#define TAILQ_EMPTY(head) ((head)->tqh_first == NULL)
#define TAILQ_FIRST(head) ((head)->tqh_first)
#define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

#define TAILQ_LAST(head, headname)                                             \
  (*(((struct headname*) ((head)->tqh_last))->tqh_last))
#define TAILQ_PREV(elm, headname, field)                                       \
  (*(((struct headname*) ((elm)->field.tqe_prev))->tqh_last))

/*
 * Circular queue definitions.
 */
#define CIRCLEQ_HEAD(name, type)                                               \
  struct name {                                                                \
    struct type* cqh_first; /* first element */                                \
    struct type* cqh_last;  /* last element */                                 \
  }

#define CIRCLEQ_HEAD_INITIALIZER(head)                                         \
  { (void*) &head, (void*) &head }

#define CIRCLEQ_ENTRY(type)                                                    \
  struct {                                                                     \
    struct type* cqe_next; /* next element */                                  \
    struct type* cqe_prev; /* previous element */                              \
  }

/*
 * Circular queue functions.
 */
#define CIRCLEQ_INIT(head)                                                     \
  do {                                                                         \
    (head)->cqh_first = (void*) (head);                                        \
    (head)->cqh_last  = (void*) (head);                                        \
  } while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field)                        \
  do {                                                                         \
    (elm)->field.cqe_next = (listelm)->field.cqe_next;                         \
    (elm)->field.cqe_prev = (listelm);                                         \
    if ((listelm)->field.cqe_next == (void*) (head))                           \
      (head)->cqh_last = (elm);                                                \
    else                                                                       \
      (listelm)->field.cqe_next->field.cqe_prev = (elm);                       \
    (listelm)->field.cqe_next = (elm);                                         \
  } while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field)                       \
  do {                                                                         \
    (elm)->field.cqe_next = (listelm);                                         \
    (elm)->field.cqe_prev = (listelm)->field.cqe_prev;                         \
    if ((listelm)->field.cqe_prev == (void*) (head))                           \
      (head)->cqh_first = (elm);                                               \
    else                                                                       \
      (listelm)->field.cqe_prev->field.cqe_next = (elm);                       \
    (listelm)->field.cqe_prev = (elm);                                         \
  } while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_HEAD(head, elm, field)                                  \
  do {                                                                         \
    (elm)->field.cqe_next = (head)->cqh_first;                                 \
    (elm)->field.cqe_prev = (void*) (head);                                    \
    if ((head)->cqh_last == (void*) (head))                                    \
      (head)->cqh_last = (elm);                                                \
    else                                                                       \
      (head)->cqh_first->field.cqe_prev = (elm);                               \
    (head)->cqh_first = (elm);                                                 \
  } while (/*CONSTCOND*/ 0)

#define CIRCLEQ_INSERT_TAIL(head, elm, field)                                  \
  do {                                                                         \
    (elm)->field.cqe_next = (void*) (head);                                    \
    (elm)->field.cqe_prev = (head)->cqh_last;                                  \
    if ((head)->cqh_first == (void*) (head))                                   \
      (head)->cqh_first = (elm);                                               \
    else                                                                       \
      (head)->cqh_last->field.cqe_next = (elm);                                \
    (head)->cqh_last = (elm);                                                  \
  } while (/*CONSTCOND*/ 0)

#define CIRCLEQ_REMOVE(head, elm, field)                                       \
  do {                                                                         \
    if ((elm)->field.cqe_next == (void*) (head))                               \
      (head)->cqh_last = (elm)->field.cqe_prev;                                \
    else                                                                       \
      (elm)->field.cqe_next->field.cqe_prev = (elm)->field.cqe_prev;           \
    if ((elm)->field.cqe_prev == (void*) (head))                               \
      (head)->cqh_first = (elm)->field.cqe_next;                               \
    else                                                                       \
      (elm)->field.cqe_prev->field.cqe_next = (elm)->field.cqe_next;           \
  } while (/*CONSTCOND*/ 0)

#define CIRCLEQ_FOREACH(var, head, field)                                      \
  for ((var) = ((head)->cqh_first); (var) != (const void*) (head);             \
       (var) = ((var)->field.cqe_next))

#define CIRCLEQ_FOREACH_REVERSE(var, head, field)                              \
  for ((var) = ((head)->cqh_last); (var) != (const void*) (head);              \
       (var) = ((var)->field.cqe_prev))

/*
 * Circular queue access methods.
 */
#define CIRCLEQ_EMPTY(head) ((head)->cqh_first == (void*) (head))
#define CIRCLEQ_FIRST(head) ((head)->cqh_first)
#define CIRCLEQ_LAST(head) ((head)->cqh_last)
#define CIRCLEQ_NEXT(elm, field) ((elm)->field.cqe_next)
#define CIRCLEQ_PREV(elm, field) ((elm)->field.cqe_prev)

#define CIRCLEQ_LOOP_NEXT(head, elm, field)                                    \
  (((elm)->field.cqe_next == (void*) (head)) ? ((head)->cqh_first) :           \
                                               (elm->field.cqe_next))
#define CIRCLEQ_LOOP_PREV(head, elm, field)                                    \
  (((elm)->field.cqe_prev == (void*) (head)) ? ((head)->cqh_last) :            \
                                               (elm->field.cqe_prev))

#endif /* sys/queue.h */
